The Xfinity 500 Round of 8 Playoff from Martinsville (Va.) Speedway determines the last two berths for next week's Championship 4 in Phoenix. Christopher Bell (No. 20 car) and Kyle Larson (No. 5) enjoy big points cushions to start the race, while William Byron (No. 24), Joey Logano (No. 22), Ryan Blaney (No. 12) and Chase Elliott are likely in need of a checkered flag to keep title hopes alive.